Hi,
I was stumped by this. The two S4 objects below looked exactly the same:
> a1
An object of class "A"
Slot "aa":
integer(0)
> a2
An object of class "A"
Slot "aa":
integer(0)
> str(a1)
Formal class 'A' [package ".GlobalEnv"] with 1 slots
..@ aa: int(0)
> str(a2)
Formal class 'A' [package ".GlobalEnv"] with 1 slots
..@ aa: int(0)
But they were not identical:
> identical(a1,a2)
[1] FALSE
Then I found that one had a "names" attribute but not the other:
> names(attributes(a1))
[1] "aa" "class" "names"
> names(attributes(a2))
[1] "aa" "class"
> names(a1)
NULL
> names(a2)
NULL
Which explained why they were not reported as identical.
After tracking the history of 'a1', I found that it was created with
something like:
> setClass("A", representation(aa="integer"))
[1] "A"
> a1 <- new("A")
> names(a1) <- "K"
> names(a1)
NULL
So it seems that, by default (i.e. in the absence of a specialized
method), the `names<-` primitive is adding a "names" attribute to the
object. Could this behaviour be modified so it doesn't alter the object?
Thanks,
H.
--
Hervé Pagès
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024
E-mail: hpa...@fhcrc.org
Phone: (206) 667-5791
Fax: (206) 667-1319
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